Quality inspection is an important component of a production line. Defects in products that are not detected in the production plant, and that find their way to a customer, may cause significant problems or inconvenience to the customer, as well as damage to the reputation of the manufacturer.
For example, a production line may be configured to produce ceramic tiles. Defects in a tile may include cracks or scratches, or areas that have been colored with the wrong hue. Defects may be caused by failure of one or more components of the production line. Failure to detect a defect in the production line soon after the appearance of the failure may result in the production of a large quantity of defective tiles. Detection of the defects at a later stage, such as during a final inspection or during inspection by a customer receiving a shipment of tiles may result in rejection of a large quantity of tiles. Therefore, it is desirable to include an inspection step in a production line.
An inspection apparatus employed in an inspection step of a production should be such as to enhance the ability of an operator to detect defects with a large degree of reliability and consistency. For example, the apparatus may be configured to enhance the ability to distinguish a surface defect against a background of intentional or acceptable surface features. Such an inspection apparatus on a production line may result in immediate detection of defects as they are formed, possibly enabling immediate adjustment of production parameters so as to prevent formation of further defects. For example, illumination of the surface may be such as to emphasize surface defects. In some cases, an inspection apparatus may include an imaging system and image processing in order to identify defects. For example, Bose et al. in U.S. Pat. No. 4,975,972 describe surface inspection in which image processing is used to adjust gray scale levels so as to isolate an image of a defect from the remainder of an acquired image. Other systems, such as those described by Clarke et al. (U.S. Pat. No. 5,168,322) and Jordan, III et al. (U.S. Pat. No. 5,864,394) utilize comparisons between acquired images, typically in nominally flat surfaces. Nater et al. in U.S. Pat. No. 3,667,846 describes an apparatus for measuring microscopic height differences in a surface.
An apparatus for enhancing the ability to inspect products in a production line may be particularly useful for detection of surface geometrical defects in products containing possibly textured flat facets. However, implementing such enhanced inspection may be difficult. For example, a single production line may produce a family of similar products, but with significant differences among the individual products. In such a case, it may be difficult to configure a general purpose apparatus for enhancing inspection of all products produced by the production line. For example, a production plant for producing ceramic tiles may be used to produce a wide variety of tile designs containing a variety of surface finishes. For example, at one extreme a polished, glossy, or shiny surface that reflects light specularly, and at the other extreme, a matte surface may reflect light diffusively.
In addition, a product surface may be intentionally designed with texture or with raised geometrical patterns or other designs in relief. A detection system must be configured to enable distinguishing such intentional surface features from surface defects. For example, a production line for the production of ceramic tiles may be used to produce various tile designs where the intentional patterning may vary from design to design. In addition, a single tile design may include acceptable variations in patterning that may vary from tile to tile.
Existing inspection systems are often not configurable for a wide variety of product surfaces. As a result, such systems may not detect defects in the surface of a given product design with sufficient reliability. Such systems may yield false positive (detection of a defect where none exists) or false negative (failure to detect an existing defect) results. False positive results may result in unnecessarily delays in production, or in ignoring the results yielded by the inspection system. False negative results may result in production of an unacceptably large number of defective products.
On the other hand, reconfiguring an inspection system for inspection of a different product design may typically involve extensive retooling or reprogramming of the system. Thus, the scope of application of such a system may be limited to specific defects on a specific type of surface.
Thus, there is a need for an inspection system that enhances the ability to distinguish between intentional surface features and surface defects, and which may be readily and reproducibly reconfigured for inspecting a wide variety of surface types.
It is an object of the present invention to provide a surface scanning system that is configurable to detect defects of different characteristics in a variety of surface types.
Other aims and advantages of the present invention will become apparent after reading the present invention and reviewing the accompanying drawings.